"electric cars are much more efficient than gasoline-powered vehicles" Actually they're not.
"gasoline has 40x the energy per gram, compared to lithium batteries" and these batteries cost $100/lb. Lead acid batteries are 400x less efficient than gas by weight.
http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/physics%2010%20notes/Electric%20cars%20.html

Perhaps what they meant is how much of the energy from the gasoline is actually used by the car rather than lost through the heat. With batteries most of the energy from the batteries is used by the car and thus is more efficient than gasoline in which only around 30 percent of the energy is actually used while the rest is lost through heat. However if you're just talking about pure energy, gasoline has more energy per weight than battery. Same reason why jet fuel is very very very expensive because per weight, it provides a lot of energy.

except electric car batteries aren't made out of lithium........
if they were, they would weigh much, much more.
i don't know where you got that from, but most electric cars use a type of lanthanum battery that is much more weight efficient.
gas powered car are very inefficient, they only use about 20% of the generated energy. Compared to the nickel metal hydride(lanthanum + mixture of other metals) battery with an efficiency of about 70%. Most electrical cars require gas to run and the energy also comes from inefficient powerplants, so that bring the efficiency down a bit. The electrical cars are still more efficient though.